Conventionally, there is known a collision determination device which is provided with wall side acceleration sensors disposed in right and left side walls of a vehicle and with a central acceleration sensor (safing sensor) disposed at a central part of the vehicle. For example, refer to Japanese Laid-Open Patent Application No. 11-180249.
In this collision determination device, the integral of an acceleration detected by each of the wall side acceleration sensors and the central acceleration sensor is calculated, and when the integral value exceeds a predetermined threshold, a comparator outputs the comparison result in order to initiate a passenger protection unit in the vehicle.
However, in the above-mentioned collision determination device, if the predetermined threshold is changed to a larger value in order to prevent the malfunction of the passenger protection unit, there is a problem that the passenger protection unit is not initiated at the time the passenger protection unit should be initiated because of the larger threshold value.
On the other hand, if the predetermined threshold is changed to a smaller value in order to obviate the above-mentioned inoperability of the passenger protection unit, there is a possibility that the malfunction of the passenger protection device is caused because of the smaller threshold value.
Moreover, the position where the central acceleration sensor is disposed in the vehicle is farther from the position where the impact of side collision is exerted on the vehicle than the positions in which the side wall acceleration sensors are disposed. Therefore, there is a possibility that the judgment of the acceleration detected by the central acceleration sensor based on the threshold is delayed from the judgment of the acceleration detected by the side wall acceleration sensors based on the threshold.
Furthermore, the acceleration detected by the central acceleration sensor may have the amount of attenuation that is larger than that of the acceleration detected by the side wall acceleration sensors. For this reason, there is a problem that the accuracy of judgment of the acceleration detected by the central acceleration sensor based on the threshold is degraded, which may cause the malfunction of the passenger protection device.